Shingle Roofing Valley Flashing: Your Guide to Doing It Right

When water drains off your roof, it moves quickly—especially through valleys, where two slopes meet. That’s why valley flashing is one of the most critical components of any asphalt shingle roof. If you’re a homeowner in Gainesville or surrounding towns like Cumming, Buford, or Dahlonega, here’s what you need to know to make sure your roof valleys are done right—and built to last.

What Is Valley Flashing?

Valley flashing is a protective metal layer (usually aluminum or copper) that lines the roof valley. Its job? To channel water off the roof and into your gutter system—without allowing any to seep under your shingles.

Common Types of Valley Installation

At L&L Roofing & Construction, we use different valley methods depending on your home’s roof design and slope:

1. Open Valley (Recommended)

• Exposes a 6"–10" wide metal flashing strip.

• Provides the best protection against water, ice, and debris.

• Ideal for high-wind and heavy-rain areas like North Georgia.

• Flashing pieces should overlap at least 12", with lower pieces underneath.

2. Closed-Cut Valley

• Shingles from one roof plane are laid across the valley.

• The top layer from the opposite side is cut to form a clean line.

• Effective when installed correctly, but prone to leaks if not sealed at the cut.

3. Woven Valley

• Shingles are woven together in the valley.

• Not recommended for laminated or architectural shingles due to thickness.

• Suitable only for certain low-volume water flow areas.

Key Installation Best Practices

Whether you're installing or inspecting, here’s what to watch for:

• Underlayment matters: Install a 36" self-adhering ice and water shield membrane under valley flashing for added protection.

• Don’t nail in the valley: Nails should be placed at least 6" away from the centerline to avoid puncturing critical waterproof areas.

• Clip corners: Trim top corners of shingles at a 45º angle to prevent debris buildup and promote proper water flow.

• Hemmed edges: Hemming (folding) the metal flashing edges locks in water and prevents capillary action during storms.

• Sealant where needed: Use asphalt plastic cement sparingly along shingle edges and flashing seams to prevent water intrusion.

Common Mistakes to Avoid

We’ve seen plenty of roofs that failed simply because of preventable valley issues:

• Reusing damaged or rusted flashing during a roof replacement.

• Leaving seams too close to the eaves, where snow and debris collect.

• Installing metal flashing with no hem or inadequate overlaps.

• Driving nails too close to the valley centerline.

• Skipping underlayment or using improper material beneath flashing.

Local Insight from L&L Roofing

We’ve replaced valley sections in neighborhoods across Gainesville, Dawsonville, Flowery Branch, and Coal Mountain, often due to improper original installation. Whether it’s wind-blown rain from spring storms or freeze-thaw cycles in winter, we’ve seen how valleys take the brunt of it.

Our team makes sure every valley is reinforced with high-temp ice and water shield, 24"–36" wide flashing, and smart water channeling details.

FAQs

How wide should valley flashing be?

At least 24" wide for open valleys is standard. Some situations (like steep roofs or areas with heavy rain) may require wider flashing.

Should I see the valley flashing on my roof?

Yes—if you have an open valley, the flashing should be visible and centered between the roof planes.

Can valley flashing be reused during roof replacement?

Only if it’s in excellent condition and fits the new shingle layout. Otherwise, always replace it to maintain a watertight seal.

Is closed-cut or open valley better?

Open valleys are more durable and less prone to debris buildup. They’re the preferred method in most professional applications.

If your roof valleys are leaking, sagging, or just outdated, don’t wait. Let our crew at L&L Roofing take a look and give you honest, practical recommendations—backed by integrity and years of hands-on experience.